A mysterious radiation release that has indefinitely shuttered a nuclear waste dump in New Mexico may have been caused by a change in the type of kitty litter that is mixed with the toxic waste.

That's one of the theories that officials are exploring as they investigate the February 14 leak at the Waste Isolation Pilot Project in southeastern New Mexico that contaminated 21 workers with low levels of radiation.

Jim Conca, a scientist who worked at the facility from 2000 to 2010, said believes a change from non-organic to organic litter caused a chemical reaction inside a waste drum, releasing the radioactive isotopes.

Mystery leak: The Waste Isolation Pilot Plant near Carlsbad, N.M., became the site of a radiation leak in February

New Mexico Environment Department Secretary Ryan Flynn confirmed to the Carlsbad Current-Argus Monday that he has heard Department of Energy officials discuss the possibility that kitty litter may have been to blame for the radiation leak.

Flynn said it is one of many theories and nothing is certain at this time.

In a statement Tuesday, the DOE said only that it is investigating 'all possible scenarios.'

The dump 26 miles east of Carlsbad cannot take in liquid waste, so kitty litter is used to absorb any fluids before drums of waste are sealed and shipped to the facility, Conca said.

One of a kind: In this March 7, 2014 photo released the U.S. Department of Energy, specially-trained workers make unmanned tests inside the shuttered Carlsbad facility - the nation's only underground nuclear waste dump

The dump is the federal government's only permanent deep-underground repository for waste from decades of building nuclear bombs from Los Alamos National Laboratories and other federal facilities.

WIPP Recovery Manager Jim Blankenhorn told a town hall meeting last week that after several trips into the half-mile-deep repository, officials believe the radiation leak was likely caused by a chemical reaction in nuclear waste that was mixed with nitrate salt.

Blankenhorn said a switch from a non-organic substance to organic was what triggered the event.

The unidentified substance containing elements mirroring nitrate salt is kitty litter, Conca said. The DOE on Tuesday confirmed that any waste with liquid is typically treated with 'an absorbent like kitty litter.'

'I'm just dying to know why this happened and who approved it, because it was a dumb idea,' Conca said. 'You just can't make a change to the procedure without reviewing it.'

Surprise culprit: A scientist believes a change from non-organic to organic kitty litter used to absorb liquid waste caused a chemical reaction

This May 10, 2014 photo provided by the Waste Isolation Pilot Plant shows waste stacks in a storage room with broken magnesium oxide bags and heat damage, seen as black streaks on the rim of the container at center, on top of a standard waste box

Investigators have said that crews on the latest trip into the mine spotted melted plastic and rubber on some drums and boxes of waste, indicating there was some kind of heat generated in the room where the waste is stored.

Nine days before the release, a truck hauling salt in the mine caught fire. But officials have said the fire was far from the waste-handling area and that the events were likely unrelated.

Initial investigations into both accidents have blamed them on poor management, an eroding safety culture, ineffective maintenance and a lack of proper oversight at the 15-year-old, $5billion site.

The Department of Energy's investigation, the results of which were made public late last month, found shortcomings at almost every step, from a more than 10-hour response to the initial emergency alarm to a bypass in the filtration system that allowed the radiation to escape above ground.

Sub-standard: A preliminary investigation has blamed the accident on poor management and an eroding safety culture

'The bottom line is they failed to believe initial indications of the release,' board chairman Ted Wyka said at a town hall meeting April 23.

DOE's report also found that much of the operation failed to meet standards for a nuclear facility; a lack of proper safety training and emergency planning; lagging maintenance; and a lack of strategy for things like the placement of air monitors.

Problems with oversight by the Department of Energy also were cited.

Bob McQuinn, who took over as head of the contractor that runs the plant shortly after the release, acknowledged mistakes by Nuclear Waste Partnership.

He also detailed a series of changes in management, training and operations to "assure that every hazard that is posed by WIPP is examined" and proper safeguards are put in place to make the operation 'a world-class nuclear operation.'